(1) Field of the Invention
The present invention relates to a method of manufacturing a honeycomb extrusion die used for extruding a ceramic honeycomb structural body and a honeycomb extrusion die manufactured according to this method.
(2) Prior Art Statement
Generally, as a die for extruding a ceramic honeycomb structural body, a honeycomb extrusion die is known in which a plurality of intersecting slits are arranged in a front surface of a die base metal and a plurality of raw material feeding holes communicated with the slits are arranged in a back surface of the die base metal. In such a honeycomb extrusion die, in order to improve a wear resistance of the slits, there is disclosed a technique in JP-A-60-145804 in which at least a part of the die base metals defining the slits is formed by coating iron boride, chromium carbide, aluminum oxide, titanium carbide, titanium nitride or titanium nitride carbide by means of CVD (chemical vapor deposition).
However, in the case that a TiN layer and a TiCN layer are to be formed successively on the die base metal made of for example martensite stainless steel by utilizing the CVD technique, it is known that, if a thickness of the TiN layer or the TiCN layer becomes thicker, a chipping (film peeling off after film formed) is easily generated. This chipping is easily generated particularly at round (R) portions formed by rounding corner portions of the die base metal defining the slits. If the chipping is generated, a coating defect occurs. Therefore, there is a problem such that a productivity of the ceramic honeycomb structural body becomes worse.
On the contrary, the applicant discloses a technique not for eliminating the chipping generation but for narrowing a slit width of the die base metal, in JP-A-10-309713, such that an electroless plating layer made of for example Ni is formed on the die base metal and the TiCN layer and a W2C layer is formed on the electroless plating layer by means of CVD. However, if this technique is utilized for eliminating the chipping generation, there occurs following problems. That is, P is included in the electroless plating layer made of for example Ni as an impurity. Therefore, if the TiN layer and the TiCN layer are formed on the electroless Ni-P plating layer by CVD, the plating layer and the CVD layer are reacted and it is not possible to obtain normal TiCN particles.
An object of the present invention is to eliminate the drawbacks mentioned above and to provide a method of manufacturing a honeycomb extrusion die and a die according to this method in which a coating layer with no chipping can be formed on a die base metal and a productivity of a ceramic honeycomb structural body during an extrusion operation can be improved.
According to a first aspect of the invention, a method of manufacturing a honeycomb extrusion die comprises the steps of: preparing a die base metal in which a plurality of intersecting slits are arranged in a front surface thereof and a plurality of raw material feeding holes communicated with the slits are arranged in a back surface thereof; forming a plating layer on the die base metal by means of electrolytic plating; and forming a TiCN layer on the plating layer by means of CVD (chemical vapor deposition).
Moreover, according to a second aspect of the invention, a method of manufacturing a honeycomb extrusion die comprises the steps of: preparing a die base metal in which a plurality of intersecting slits are arranged in a front surface thereof and a plurality of raw material feeding holes communicated with the slits are arranged in a back surface thereof; forming a plating layer on the die base metal by means of electrolytic plating; forming a TiN layer on the plating layer by means of CVD (chemical vapor deposition); and forming a TiCN layer on the TiN layer by means of CVD.
Further, according to the invention, a die manufactured according to the first aspect of the second aspect of the method of manufacturing the honeycomb extrusion die, comprises: (1) a die base metal having slits and raw material feeding holes; a plating layer formed on the die base metal; and a TiCN layer formed on the plating layer, or, (2) a die base metal having slits and raw material feeding holes; a plating layer formed on the die base metal; a TiN layer formed on the plating layer; and a TiCN layer formed on the TiN layer.
In the present invention, since the electrolytic plating layer is arranged between the die base metal and the TiCN layer or between the die base metal and the TiN layer, a contact property therebetween can be improved, so that the chipping is not easily generated if a thickness of the film is thicker. Moreover, since the plating layer is made of the metal and the metal has an excellent stiffness, it is possible to reduce a heat stress between the die base metal and the TiCN layer or the TiN layer, and thus the chipping is not easily generated. Further, since an impurity in the electrolytic plating layer is very little, it is possible to obtain normal TiCN particles.
In the preferred embodiment of the method of manufacturing the honeycomb extrusion die according to the invention, the plating layer is made of Ni, Co, Cu or transition metals which are not easily nitrided or oxidized, and a thickness of the plating layer is not less than 0.01 xcexcm. In the both embodiments, it is possible to achieve the present invention more effectively, and thus they are preferred.